1. Field of the Art
This invention relates to a mechanical radial scan type ultrasound probe with an ultrasound transducer element to be rotated within an intracorporeal or intracavitary portion for examination or diagnostic purposes.
2. Prior Art
Ultrasound diagnosis systems which are currently in use for medical examinations are often equipped with the so-called mechanical radial, scan type ultrasound probes which are designed to be inserted into an intracavitary portion of human body. The ultrasound probes of this sort have an ultrasound transducer element connected to a rotational drive means thereby to put the ultrasound transducer element in rotation while transmitting ultrasound pulses into an intracavitary wall portion of interest at predetermined angular intervals and receiving return echoes for stratigraphic images of intracavitary wall tissues. The return echo signals thus received by the ultrasound transducer element are sent to a signal processor in a control section of an ultrasound image observation unit to form video signals of an ultrasound picture image through predetermined signal processing operations for display on a monitor.
In mechanical radial scan operations, one frame of ultrasound picture image is obtained on each revolution of the ultrasound transducer element, starting from a preset initial scan position. Namely, ultrasound picture signals for one frame of ultrasound image are produced as the ultrasound transducer element is turned through 360.degree. from a predetermined initial scan position, and the single-frame ultrasound picture signals are converted into video signals to display a video image on a monitor screen. For this purpose, the signal processor includes a scan converter with a memory for storing the ultrasound echo signals, which are received through the ultrasound transducer element, along with angular position signals from an angular position detection means which detects rotational angles of the ultrasound transducer element. The stored echo signals are converted into video signals as they are read out from the memory.
In a radial ultrasound scanning.operation, an ultrasound image is displayed by means of a large number of acoustic lines which are arranged radially and successively at predetermined angular intervals through 360.degree. from a scan initiating end position corresponding to a predetermined original position on the monitor screen. These acoustic lines correspond to the ultrasound echo signals which are sampled at predetermined time intervals along the time axis. Therefore, although the time differential between two adjacently adjoining acoustic lines is ignorably small, it gradually increases to bring about an appreciable discrepancy between the acoustic lines at the initial and terminal end positions of the 360.degree. scan field. More specifically, since an intracavitary organ under examination is usually in motion, an appreciably large time differential makes it difficult to match the ultrasound image segments of the initial and terminal acoustic lines which are sampled in different phases in time. Namely, it causes a discontinuity in ultrasound picture image across the initial and terminal acoustic lines of the 360.degree. scan field. Such a discontinuity in picture image could occur to a region of special interest, making it difficult for the operator to go into a close examination of that region. Of course, the initial scan position of the ultrasound probe relative to a particular intracavitary region can be adjusted by changing the position of the ultrasound probe itself. within an intracavitary portion. However, such re-positioning of the entire body of the inserted ultrasound probe could result in unexpectedly large deviations of the ultrasound transducer element from an intracavitary portion of interest.